1. Field of the Invention
The present invention relates to a solid-state image pickup element and a driving method thereof, and particularly to a single plate type color solid-state image pickup element and a driving method thereof.
2. Description of the Related Art
In a related-art single plate type color solid-state image pickup element such as a CCD (Charge Coupled Device) image sensor, a CMOS (Complementary Metal Oxide Semiconductor) image sensor, a color filter transmitting red, green, or blue is disposed above a light receiving/charge accumulating layer. In order to obtain color video information, visible light transmitted by the color filter and received by the light receiving/charge accumulating layer is output as a signal from the solid-state image pickup element. The color filter of each color absorbs about ⅔ of incident light. There are thus disadvantages of poor efficiency of use of visible light and low sensitivity. In addition, because each solid-state image pickup element provides a color signal of only one color, there are other disadvantages of poor resolution and noticeable false color, in particular.
Accordingly, in order to overcome such disadvantages, a solid-state image pickup element in which three light receiving/charge accumulating layers are laminated has been studied and developed (see Japanese Patent Laid-Open No. 2006-278446, for example). The solid-state image pickup element of such a structure has a pixel structure in which three light receiving/charge accumulating layers for generating charges with respect to light of the three primary colors of blue, green, and red are laminated in order from a light incidence surface, for example. Each solid-state image pickup element has a signal reading circuit for reading the charges generated in the respective light receiving/charge accumulating layers independently, and performs photoelectric conversion on most of incident light. Therefore, the efficiency of use of visible light is close to 100%, and signals corresponding to the three primary colors of blue, green, and red are obtained by one solid-state image pickup element. There is thus an advantage in that an excellent image of high sensitivity and high resolution is obtained.